| Abstract |
The application of different heat transfer surface extension techniques to improve the performance of an air-cooled heat exchanger is examined. Particularly, our case study focuses on a Solar Enhanced Natural Draft Dry Cooling Tower (SENDDCT) designed by Queensland Geothermal Energy Centre of Excellence (QGECE), as the air-cooled condenser of a geothermal power plant. The conventional method of extending the heat transfer area by means of fins is compared with a modern technique being the application of a thin metal foam layer to the outer surface of the tube. Both fins and foams lead to heat transfer augmentation, from the cycle fluid flowing in the tube bundle, albeit at the expense of a higher pressure drop when compared to the bare tube bundle as our reference case. Aiming at maximizing the heat transfer enhancement and minimizing the total pressure drop, the two heat transfer surface extension techniques are compared against each other and an optimal solution is obtained. Different tube bundle layouts and tube spacing are examined. Sensitivity analysis was conducted to investigate the effect of sunroof diameter on the overall performance of the system. Aiming at minimizing the flow and thermal resistances for a SENDDCT, an optimum design is presented for an existing tower to be equipped with solar panels to afterheat the air leaving the heat exchanger bundles arranged vertically around the tower skirt. A number of correlations are also proposed to predict the total pressure drop and heat transfer of the extended surfaces considered here. |